This proposal is in response to the BIOBEHAVIORAL PAIN RESEARCH RFA PA-99-021. It is a COMPETING CONTINUATION application for grant NS 35115 funded from 5-1-96 to 4-30-99. In the last funding period we developed a new functional brain imaging paradigm, using functional magnetic resonance imaging (fMRI), that enables us to parcel cortical activity associated with painful stimuli along a stimulus-suffering from chronic Reflex Sympathetic Dystrophy (RSD) pain show prefrontal hyperactivity. These abnormal activations are reversed to that seen in normal subjects after a sympathetic block. Given the new paradigm and our observations in chronic pain patients and normal volunteers we propose to extend the studies to extend the studies of the pathophysiology of chronic pain by testing specific hypotheses, designed to distinguish between two chronic pain states: Specific Aim 1 tests the hypothesis that chronic low back pain with radicular involvement can be differentiated from acute low back pain, and from normal subjects by functional brain imaging studies. These studies are designed to image brain activity directly related to the pain from which the patients suffer. The acute back pain patients are studied before and three months after spinal cord surgery. Specific Aim 2 tests the hypothesis that chronic RSD pain with allodynia is distinct from chronic RSD pain with only hyperalgesia, and that chronic RSD pain is distinguishable from chronic low back pain. The studies are done using fMRI and again are designed to directly study the pain from which the patients suffer. Specific Aim 3 tests the hypothesis that chronic pain states are associated with brain biochemistry abnormalities, and that different chronic pains may be differentiated by brain biochemistry. Hydrogen-Magnetic Resonance Spectroscopy (MRS) will be used to examine different brain regions and chemicals in RSD and low back pain patients and compared to normal subjects. Specific Aim 4 tests the hypothesis that chronic pain is correlated with cognitive abnormalities. RSD and back pain patients will be tested on a battery of cognitive tests: Stroop, WCST, and Bechara's Gambling test. The chosen tests examine different frontal abilities and may differentiate between types of chronic pain. Overall the studies are designed to examine chronic pain by functional imaging, brain biochemistry, and cognitive abilities. The results, if successful, have the potential of being used in the clinic as diagnostic or prognostic tools.